1. Field of the Invention
The present invention relates to digital communication systems, and more particularly to a method and an apparatus for blind detection, for example, used in an EGPRS system, and a wireless communication receiver including the same.
2. Description of the Related Art
Enhanced Data rates for GSM Evolution (EDGE) is a radio-based high-speed mobile data standard that can be integrated into GSM/GPRS and IS-136 networks. Enhanced Data rates for GSM Evolution (EDGE), and a related packet service, i.e. Enhanced General Packet Radio Service (EGPRS), are currently being applied to mobile communication standards, such as Global System for Mobile communications (GSM), General Packet Radio Service (GPRS) and Universal Mobile Telecommunications System (UMTS).
In the EDGE technology, a data rate of a wireless channel varies according to the performance of a receiver. The data (transmission) rate may be varied by modifying a modulation method (modulation mode) and/or an encoding method.
In the modulation method of varying the data rate, a Gaussian Mean Shift Keying (GMSK) modulation mode is used in GSM, and an Eight Phase Shift Keying (8-PSK) modulation mode is used in EGPRS. GSM originally used GMSK modulation and robust channel coding only. To achieve higher data rates in case of good physical channels, GPRS and later EDGE were introduced. In contrast to GPRS, EDGE additionally uses the 8-PSK modulation mode.
Because a base station (transmitter) does not transmit any information about the modulation mode currently being used in the EGPRS, the receiver must perform a blind detection for determining the modulation mode. The training sequence code (TSC) based channel estimation is done before equalization.
The blind detection is a procedure for determining the current modulation mode from received data. The receiver uses a training sequence code (TSC) of a normal burst of the received data to perform the blind detection. In the mobile communication standard GSM/EDGE, the base station can select one of eight training sequence codes 0 through 7 as a midamble (symbols 61 through 86) of the downlink transmitted bursts. (See FIG. 6).
FIG. 1 is a conceptual diagram illustrating a conventional method of blind detection.
Referring to FIG. 1, the training sequence code TSC is represented as a symbol 61 through a symbol 86 (among symbols 0 through 147). The receiver stores phase differences Δφ′62 through Δφ′86 between neighboring symbols in a stored (previously-known) training sequence code (symbol 61 through symbol 86)
Herein, the symbol Δφ′62 represents a phase difference between the symbol 62 and the adjacent symbol 61, and the symbol Δφ′86 represents a phase difference between the symbol 86 and the symbol 85.
Then, the receiver detects (e.g., measures) phase differences Δφ1 through Δφ147 (including Δφ62 through Δφ86) between neighboring symbols of a current (received) training sequence code.
Assuming that phase differences between neighboring symbols of the received training sequence code are represented by Δφ′62 through Δφ′86 in a GSMK modulation mode and that phase differences between neighboring symbols of the current (stored) training sequence code are represented by Δφ′62 through Δφ′86 in a GSMK modulation mode, a sum of absolute values of the phase differences Δψ′ and Δψ (between received and stored training sequence codes) satisfies the following Equation 1:
                                          ∑                          n              =              62                        86                    ⁢                                                (                                                Δφ                  n                                -                                  Δφ                  n                  ′                                            )                                                  ≈        0                            [                  Equation          ⁢                                          ⁢          1                ]            
However, when the current modulation mode is an 8-PSK modulation mode, the sum of absolute values of the phases differences Δψ′ and Δψ (between received and stored training sequence codes) does not satisfy Equation 1.
Therefore, the receiver determines that the current modulation mode is the GMSK modulation mode, (i.e., a GSM mode) when Equation 1 is satisfied, and determines that the current modulation mode is the 8-PSK modulation mode, (i.e., EGPRS mode) when Equation 1 is not satisfied.
Because the conventional blind detection method has to compare the phase differences Δφ′62 through Δφ′86 between neighboring symbols of the stored (previously-known) training sequence code with the phase differences Δφ62 through Δφ86 between neighboring symbols of the current (currently received) training sequence code, the receiver performs a large number of calculations, and as a result, requires a long time to perform the blind detection.